1. Field of the Invention
The present invention relates to a photographic flash device to be used to project an artificial light for photographing, and more particularly to a photographic flash device capable of using for photographing with lenses of various focal lengths.
2. Background of the Invention
Generally speaking, a photographic flash device should project light with angle of divergence corresponding to angle of photography of a photographing lens used. Namely, for a photographing by standard lens the angle of divergence of the flash light should be of medium, for photographing by a telephoto lens the angle of divergence of the flash light should be narrower than the standard case in order to save the light not to wastely illuminate surrounding part around a real photographic object for the telephoto lens and to concentrate, and hence strengthen, the light intensity for the real photographic object, and for a photographing by wide angle lens the angle of divergence of the flash light should be wider than the standard case in order not to fail illuminating peripheral part of a photographic object.
It is known that a longest distance for which a photographing can be made and an angle of divergence of flashed light are inversely related. Namely, when the angle is the narrower, the light is the more concentrated, and hence enables photographing of the farer object, and when the angle is the wider a photographing is limited to the nearer object.
For the abovementioned reason, in order to enable flash illumination for photographing by various lenses, some improvements have been proposed. One example of such conventional improvement is to provide a flash device with several movable reflection mirrors which are to be moved for obtaining lights of various divergence angles. Another example of the conventional improvement is to provide a flash device with detachable or exchangable converging lens(es) in front of flash tube. The former conventional improvement has a shortcoming of large size and complex construction because of including two reflection mirrors, while the latter conventional improvement has a shortcoming of necessitating several lenses and hence of possible losing of the lenses. Still another example of the conventional improvement is to provide a flash device with a detachable converging lens holded on a detachable arm, which also has a shortcoming of losing the arm and or lens and further likely damaging the lens due to an uncovered construction thereof.